Ring opening metathesis polymerisations of norbornene and norbornadiene derivatives containing oxygen: A study on the regeneration of Grubbs catalyst

Article abstract of DOI:10.1016/j.tet.2004.06.065

Ring opening metathesis polymerisation (ROMP) of norbornene and norbornadiene derivatives containing oxygen are investigated using Grubbs well-defined ruthenium initiator. A series of 7-alkoxy norbornadiene monomers (2b-d), containing alkoxy groups with decreasing steric hindrance in the 7-position have been prepared. The ROMP reactions of monomers showed that as the reaction proceeds the initiator is consumed first and then is partially regenerated at the expense of the propagating species. A small amount of another carbene species X, giving a broad signal at 17.44 ppm, is also formed which is extremely stable in solution. The species X is an active metathesis species and is able to perform ROMP on strained cyclic olefins. ROMP of monomers without alkoxy groups in the 7-position (3, 4a, 4b, 5a and 5b) and also monomers with alkoxy groups in the 5 and/or 6 positions of norbornene (6 and 7) have been performed under similar conditions. None of these systems exhibited regeneration of the initiator and no resonances due to species X can be seen in the ¹H NMR spectra. The results confirm that the presence of oxygen in the 7-position of the norbornadiene monomer plays an important role in the process of regeneration of the initiator. It is found that the steric bulk and the position of substituents of the monomer have a pronounced influence on the extent of regeneration of the initiator.

Full text of DOI:10.1016/j.tet.2004.06.065

Tetrahedron 60 (2004) 7217–7224
Ring opening metathesis polymerisations of norbornene and
norbornadiene derivatives containing oxygen: a study on the
regeneration of Grubbs catalyst
*
David M. Haigh, Alan M. Kenwright and Ezat Khosravi
Department of Chemistry, Interdisciplinary Research Centre in Polymer Science and Technology, University of Durham,
South Road, Durham DH1 3LE, UK
Received 18 May 2004; revised 11 June 2004; accepted 14 June 2004
Abstract—Ring opening metathesis polymerisation (ROMP) of norbornene and norbornadiene derivatives containing oxygen are
investigated using Grubbs well-defined ruthenium initiator. A series of 7-alkoxy norbornadiene monomers (2b–d), containing alkoxy groups
with decreasing steric hindrance in the 7-position have been prepared. The ROMP reactions of monomers showed that as the reaction
proceeds the initiator is consumed first and then is partially regenerated at the expense of the propagating species. A small amount of another
carbene species X, giving a broad signal at 17.44 ppm, is also formed which is extremely stable in solution. The species X is an active
metathesis species and is able to perform ROMP on strained cyclic olefins. ROMP of monomers without alkoxy groups in the 7-position (3,
4a, 4b, 5a and 5b) and also monomers with alkoxy groups in the 5 and/or 6 positions of norbornene (6 and 7) have been performed under
similar conditions. None of these systems exhibited regeneration of the initiator and no resonances due to species X can be seen in the 1H
NMR spectra. The results confirm that the presence of oxygen in the 7-position of the norbornadiene monomer plays an important role in the
process of regeneration of the initiator. It is found that the steric bulk and the position of substituents of the monomer have a pronounced
influence on the extent of regeneration of the initiator.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
(ADMET).9 They have also found many applications in the
synthesis of natural products.10–12
The olefin metathesis reaction has become an invaluable
synthetic tool for chemists. The ability to simultaneously
cleave and reform carbon–carbon double bonds has led to its
widespread use in the design of useful organic molecules1
and polymers.2
Schrock introduced well-defined molybdenum initiators
with bulky alkoxide and arylimido ligands of the type
Mo(CHR)(NAr)(OR0)2 [R¼–CMe3 and R0¼–CMe3 or
–C(CF3)2Me] which allowed a high degree of control of
molecular weight, polydispersity, cis/trans content and, in
favourable cases, tacticity.13–16 The key to controlled
polymerisation is that while the molybdenum initiators are
inactive towards double bonds in the polymer chain, they
react rapidly with the strained double bonds in the monomer
to give a linear polymer. However, these catalysts are
limited by the high oxophilicity of the metal centres, which
renders them extremely sensitive to oxygen and moisture.
As a result of this, they show limited tolerance towards
functional groups, reducing the number of potential
monomers.
Although olefin metathesis was discovered as early as
1955,3 it has only achieved a leading role in synthetic
methodology in the last decade. This is mainly attributed to
advances in the field of catalysis and organometallic
chemistry, which have been heavily influenced by the
work of Grubbs4–6 and Schrock7 in developing well-defined
transition metal carbene complexes. This new generation of
catalysts are powerful tools in the field of organic reactions1
such as ring opening metathesis (ROM), ring closing
metathesis (RCM)8 and cross metathesis (CM), and in
polymerisation reactions such as ring opening metathesis
polymerisations (ROMP)2 and acyclic diene metathesis
The key to improved functional group tolerance was the
development of catalysts that react preferentially with
olefins in the presence of heteroatoms. Grubbs et al.6
synthesised ruthenium alkylidene complexes of the type
RuCl2(PCy3)2(vCHPh) [1], which are tolerant to a wide
range of functional groups such as acids, alcohols,
Keywords: NMR; Ring opening metathesis polymerisation; Ruthenium;
Regeneration; Norbornenes; Norbornadienes.
*
Corresponding author. Tel.: þ44-191-3342014; fax: þ44-191-3342051;
e-mail address: ezat.khosravi@durham.ac.uk
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.06.065

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D. M. Haigh et al. / Tetrahedron 60 (2004) 7217–7224
implying a secondary metathesis reaction. The stack plot of
the alkylidene proton region at intervals over a 12 h period
for this ROMP reaction, Fig. 2, shows these extraordinary
features, and it clearly exhibits the presence of three distinct
signals. Resonances due to alkylidene protons of 1 appear at
19.9 ppm, a propagating species (Pn) has signals at 19.38,
19.36, 19.33 ppm, and a species X appears at 17.44 ppm.
The three propagating signals (Pn) are believed to arise due
to the sensitivity of the chemical shift to the cis/trans
isomerism of the adjacent double bond and to the meso/
racemic isomerism of the adjacent dyad.18 The initiator is
visibly regenerated at the expense of the propagating species
as the reaction proceeds. This can only occur by a secondary
metathesis reaction by either an intra- or intermolecular
reaction at the living chain ends of the propagating species,
Fig. 3. In the intramolecular reactions, (Fig. 3, route a), the
end groups of a chain react to form a macrocycle,
regenerating the initiator. Whereas, in the intermolecular
reactions, (Fig. 3, route b), the end groups from two chains
react, resulting in regeneration of the initiator and a new
propagating species, which has a combined molecular
weight of the original propagating chains. GPC measure-
ments have previously been carried out to investigate this
process and unambiguously demonstrate that one or both of
these secondary metathesis reactions must take place.18
Another consequence of these intra and/or intermolecular
reactions is a decrease in the proportion of end groups in the
polymer. As expected, analysis of the resulting polymers
using 13C NMR revealed that polymer terminated with ethyl
vinyl ether after 24 h had fewer vinylic end groups than that
of polymer terminated in the same manner immediately
after all of the monomer had been consumed.18 A small
amount of another carbene species, labelled X, giving a
broad signal at 17.44 ppm, (Fig. 2), is also formed which
is extremely stable in solution. This observation of
regeneration of the initiator during a ROMP reaction was
the first of its kind and it has not been observed in any
other systems. In particular, it has not been observed in the
ROMP of 7-alkyl derivatives of norbornadiene.
Figure 1. Grubbs ruthenium benzylidene initiator and 7-alkoxy
norbornadienes.
aldehydes, esters and amides.6 Kinetic studies on these
catalysts revealed that catalyst 1 is an efficient initiator
for the ROMP of strained cyclic olefins, permitting the
incorporation of high degrees of functionality into the
resulting polymers.
ROMP reactions using well-defined initiators result in
polymers with a narrow polydispersity index (PDI,1.05–
1.2). Generally, the initiator is totally consumed and the
disappearance of the initiator alkylidene proton and the
appearance of the propagating alkylidene protons can be
seen in 1H NMR spectra. In this paper we report the ROMP
of 7-alkoxynorbornadienes, in which the initiator is first
consumed and then regenerated at the expense of the living
propagating species.
2. Results and discussions
We recently made a remarkable observation when catalyst 1
was used to initiate the polymerisation of 7-t-butoxynor-
bornadiene 2a (Fig. 1) using a monomer–initiator ratio
([M]o/[I]o) of 50.17 The reaction proceeds rapidly in CDCl3
with almost complete consumption of initiator to form
propagating ruthenium alkylidene species which are then
converted slowly, but not completely, back to initiator,
Figure 2. Stack plot showing the alkylidene region of the 1H NMR spectra for the first 12 h of the ROMP reaction of 2a initiated by 1 in CDCl3 system ([M]o/
[I]o¼50).

D. M. Haigh et al. / Tetrahedron 60 (2004) 7217–7224
7219
Figure 3. Schematic showing that secondary metathesis leads to regeneration of the initiator by (a) intramolecular cyclisation, or (b) intermolecular reactions.
2.1. The effect of the nature of the substituents on the
regeneration of the initiator
tives 3, 4a, 4b, 5a and 5b, shown in Figure 4, have been
performed under similar conditions to those described for
the ROMP of 2a initiated by 1, and the results are shown
1
In an attempt to probe the parameters which govern the
process of regeneration of the initiator, we have investigated
whether regeneration is apparent in any other ROMP
systems mediated by initiator 1. Polymerisations of
norbornene and the oxygen-containing norbornene deriva-
in Table 1. The reactions were followed by H NMR and,
although they behaved differently in terms of the rate of
monomer consumption and the amount of initiator con-
sumed, none of these systems exhibited regeneration of the
initiator. The alkylidene region (21–16 ppm) of the 1H
NMR spectra when monomers 3, 4a, 4b, 5a and 5b are
subjected to ROMP by 1 are shown in Figure 5, and it is
clear that no resonances due to species X (,17.5 ppm) can
be seen during the polymerisation of any of these
monomers.
2.2. The effect of the steric bulk of alkoxy substituents in
the 7-position of norbornadiene monomers on the
process of regeneration of the initiator
The results discussed above suggest that the presence of
oxygen in the 7-position of the norbornadiene monomer
plays an important role in the process of regeneration for the
ROMP of 2a using initiator 1. To investigate this effect, a
series of new monomers, 2b–d (Fig. 1), containing alkoxy
groups with decreasing steric hindrance in the 7-position
have been prepared. The ROMP reactions of monomers
2a–d initiated by 1 in CDCl3 were monitored by 1H NMR
spectroscopy. A spectrum was recorded every 15 min for
the first 3 h and then at appropriate periods until it was clear
that no further reaction was taking place. The alkylidene
region (21–16 ppm) of these spectra are shown in Figure 6
and they all exhibit a resonance for the residual initiator (I),
the propagating species (Pn) and the stable species X at
19.98, 19.50–18.50, and 17.5 ppm, respectively. Regenera-
tion of the initiator is observed in all of these ROMP
reactions, Table 2, and the extent of regeneration is found to
increase as the steric bulk of the substituent in the 7-position
increases. The regeneration of the initiator is believed to
be facilitated by the co-ordination of oxygen from the
propagating polymer backbone to the active ruthenium
Figure 4. Various strained bicyclic monomers.
Table 1. ROMP of monomers 3, 4a, 4b, 5a, 5ba
Monomer
Monomer consumption (h)
Initiator consumption (%)
3
,0.3b
14
1
0.8
,0.3b
34
83
95
69
91
4a
4b
5a
5b
a
Polymerisations were performed in CDCl3 at ambient temperature and
were initiated by 1 using a ratio of [M]o/[I]o¼50. [I]o¼15 mM. The
reactions were followed by 1H NMR spectroscopy. None of the reactions
exhibited regeneration of the initiator.
b
The monomer is completely consumed before the first 1H NMR of
reaction mixture is taken.

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D. M. Haigh et al. / Tetrahedron 60 (2004) 7217–7224
Figure 5. The alkylidene region (21–16 ppm) of the 1H NMR spectra when monomers (a) 3, (b) 4a, (c) 4b, (d) 5a and (e) 5b are subjected to ROMP by 1 using
a ratio of [M]o/[I]o¼50, [I]o¼15 mM at ambient temperature.
Figure 6. The alkylidene region (21–16 ppm) of the 1H NMR spectra when monomers (a) 2a, (b) 2b, (c) 2c and (d) 2d are subjected to ROMP by 1 using a ratio
of [M]o/[I]o¼50, [I]o¼15 mM at ambient temperature.
metal centre.18 If the chelating oxygen atom is at the chain
end of either the same (Fig. 7, route a) or a different
propagating species (Fig. 7, route b), then the terminal
double bond is brought into close proximity with the
ruthenium carbene and a subsequent secondary metathesis
reaction may result in the formation of macrocycles or a
polymer of increased molecular weight and regeneration of
the initiator. At the moment our hypothesis is that the
presence of bulky alkyl groups in the alkoxy substituent in
the 7-position of the monomer makes the oxygen atom more
electron rich, and hence a better electron donating moiety.19
As shown in Table 2, the polymerisation reactions of
monomers 2a–d initiated by 1 also provide information on
how the steric bulk of the substituent in the 7-position of the
norbornadiene unit affects other aspects of the polymeri-
sation process such as the rate of monomer consumption and
the consumption of initiator at the start of the reaction.

D. M. Haigh et al. / Tetrahedron 60 (2004) 7217–7224
7221
Table 2. ROMP of monomers 2a–da
Monomer
[M]o/[I]o
Monomer consumption (h)
Initial consumption of initiatorb (%)
99
Extent of regenerationc (%)
2a
2a
2a
50
25
10
1
0.5
0.25
29
27
23
93
81
2b
2b
2b
50
25
10
2
1
0.5
98
92
75
15
18
13
2c
2c
2c
50
25
10
5
3
0.75
98
92
71
6
8
10
2d
2d
2d
50
25
10
5.5
1
0.5
97
88
65
8
3
1
a
Polymerisations were performed in CDCl3 at ambient temperature and were initiated by 1 with [I]o¼15 mM.
The error associated with the extent of regeneration of the initiator is estimated to be ^5% of the quoted value. The reactions were followed by 1H NMR
spectroscopy.
b
c
Based on the 1H NMR spectrum recorded after 15 min of reaction.
Figure 7. A schematic showing that secondary metathesis reactions at the propagating chain ends can result in regeneration of the initiator. This can be
enhanced by (a) intra-, or (b) intermolecular chelation of an oxygen atom from the propagating chain end to the ruthenium metal centre. Species X does not
figure in this scheme.
It is now well established that one of the phosphine ligands
must dissociate from the ruthenium metal centre if initiation
and propagation are to occur in ROMP reactions mediated
by Grubbs catalyst.20 This dissociation makes the metal
carbene bond accessible for olefins to undergo the necessary
[2þ2]cyclo-addition reaction. The inserted monomer unit is
in close proximity to the active ruthenium carbene centre,
and its steric bulk can have a pronounced influence on the
ability of the free PCy3 ligand to re-associate to the metal
centre. One possibility is that an increase in the steric bulk in
the 7-position of the most recently inserted monomer unit
will impede the re-association of the PCy3 ligand, and hence
the active site is more accessible for subsequent addition of
monomer units. It may be for this reason that the monomer
is consumed faster when the steric bulk in the 7-position is
increased.
2.3. The effect of the [M]o/[I]o ratio on the process of the
regeneration of the initiator
The effect of the magnitude of the [M]o/[I]o ratio on the
regeneration of the initiator for the ROMP of monomers
2a–d by 1 in CDCl3 has also been studied. Table 2 shows
the results of the ROMP reactions performed on these
monomers using [M]o/[I]o¼50, 25 and 10.
The process of regeneration observed in these ROMP
systems is believed to be in competition with other
secondary metathesis reactions such as backbiting, invol-
ving internal double bonds along the backbone chains.18,20
The general trend for the ROMP reactions described in
Table 2, shows that as the [M]o/[I]o ratio is reduced the
extent of regeneration of the initiator decreases. Although
the reason for this observation is not fully understood,
it could be due to the fact that decreasing the length of
the propagating polymer chain leads to an enhancement of
the secondary metathesis reactions discussed earlier.
The amount of initiator consumed at the start of the reaction
decreases when the steric bulk of the alkoxy substituent
within the monomer is reduced. This is consistent with a
decrease in the steric bulk at the 7-position of the monomer
enhancing the rate of propagation relative to the rate of
initiation compared with a more sterically hindered
substituent.
In these systems, the rate of propagation is faster than that
of initiation.20 Therefore, with a lower concentration of
monomer in the system, less of the initiator will be

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D. M. Haigh et al. / Tetrahedron 60 (2004) 7217–7224
consumed before propagation becomes the dominant
process.
CD2Cl2 and C6D6 with [M]o/[I]o¼50 and the results are
presented in Table 3. The polarity indices of the solvents
according to Allerhand and Schleyer’s polarity scale, G, are
106, 100, and 80 respectively.22 A reduction in the polarity
of the solvent has no significant effect on the amount of 1
initially consumed by 2a or on the extent of regeneration of
the initiator, but the overall kinetics for the polymerisation
process are retarded (i.e. rate of consumption of the
monomer is reduced and the time period over which
regeneration was observed is extended). Monomer con-
sumption was fastest in CDCl3 and slowest in C6D6. This
trend indicates that an increase in the polarity index of the
solvent increases the rate at which the ROMP of 2a occurs.
It also reveals that the media in which the polymerisation of
2a is initiated by 1 plays no role in the regeneration process
itself, and that regeneration is solely due to the nature of the
monomer and the initiator present.
2.4. Species X
We have already discussed in detail the observation of
regeneration of the initiator at the expense of the propagat-
ing living chains when 7-substituted alkoxy norbornadiene
monomers are subjected to ROMP initiated by 1,17,18 and
we now consider the appearance of species X in the
alkylidene region of the 1H NMR’s. The presence of species
X during the ROMP of monomers 2a–d is clearly shown in
Figure 6. In all cases species X is stable and long-lived.
When 2d is subjected to ROMP using 1 with the ratio of
[M]o/[I]o¼50, species X is still visible in the 1H NMR
spectra one month after the start of the polymerisation, and
it is the only observable alkylidene species remaining in
solution. The disappearance of the initiator and propagating
species is consistent with the known rates of decomposition
of ruthenium alkylidene species as reported by Grubbs and
co-workers,21 and it is remarkable that species X still
remains in solution after this time. When a second batch of
2d (18 equiv.) is added to the solution, the monomer is
consumed very slowly (20 days), but the appearance of the
2.6. ROMP of 5 and/or 6 substituted norbornene
monomers
We discussed earlier that norbornadiene monomers with
alkoxy functionalities in the 7-position have been found to
facilitate the regeneration of initiator 1. We also showed that
the steric bulk of the alkoxy substituent in the monomer unit
plays a crucial role in the regeneration process. In order to
establish whether the specific position of the alkoxy
functionality within the monomer unit has any influence
on the process of regeneration of the initiator, monomers
with alkoxy groups in the 5 and/or 6 positions of norbornene
have been prepared (6, 7, Fig. 4) and subjected to ROMP
initiated by 1 in CDCl3. The polymerisations were
monitored by 1H NMR spectroscopy in the manner
described previously. The alkylidene region of the 1H
NMR spectra, shown in Figure 8, indicate that the reactions
exhibit similar behaviour to the ROMP reactions of
1
alkylidene region in H NMR remains unchanged i.e. only
species X is observed. This observation implies that X is an
active metathesis species, which is able to perform ROMP
on strained cyclic olefins.
2.5. The effect of the solvent on the regeneration of the
initiator
The effect of the solvent on the rate of regeneration of the
initiator for the ROMP of 2a using [M]o/[I]o¼50, has been
studied by performing the polymerisations in CDCl3,
Table 3. Solvent effects on the ROMP of monomer 2aa
Solvent
Regeneration time (days)
Monomer consumption (h)
Initiator consumption (%)
Extent of regenerationb (%)
CDCl3
CD2Cl2
C6D6
1.2
2.5
3
1
3.5
4.5
99
97
100
29
29
28
a
Polymerisations were performed at ambient temperature and were initiated by 1 using a ratio of [M]o/[I]o¼50. [I]o¼15 mM.
b
The error associated with the extent of regeneration of the initiator is estimated to be ^5% of the quoted value. The reactions were followed by 1H NMR
spectroscopy.
1
Figure 8. The alkylidene region (21–16 ppm) of the H NMR spectra when monomers (a) 6 and (b) 7 are subjected to ROMP by 1 using a ratio of [M]o/
[I]o¼50, [I]o¼15 mM at ambient temperature.

D. M. Haigh et al. / Tetrahedron 60 (2004) 7217–7224
7223
monomers 3, 4a, 4b, 5a and 5b initiated by 1. There is no
regeneration of the initiator, and no species X is observed.
This suggests that the specific position of the alkoxy
functionality plays a vital role in the regeneration of the
initiator and on the formation of species X when alkoxy
norbornadiene monomers are subjected to ROMP.
respectively and distilled prior to use. All other solvents
were used without prior purification.
Norbornene [3] was dried over sodium and distilled under
vacuum prior to use. Grubbs ruthenium initiator6 [1],
7-t-butoxynorbornadiene23 [2a], 7-methoxynorborna-
diene24 [2d], 5-exo,6-endo-dicarbomethoxynorbornene25
[4a], 5-exo,6-exo-dicarbomethoxynorbornene26,27 [4b],
exo,exo-N-phenyl-5,6-dicarboxyimidonorbornene28 [5a]
and exo,exo-N-phenylmethyl-5,6-dicarboxyimidonorbor-
nene28 [5b], and exo,exo-5,6-bis(methoxymethyl)norbor-
nene29 [7] were synthesized according to literature
procedures.
3. Conclusions
The ROMP reactions of 7-alkoxy norbornadiene monomers
(2b–d), using Grubbs well-defined ruthenium initiator
showed that as the reaction proceeds the initiator is
consumed first and then is partially regenerated at the
expense of the propagating species. This is believed to occur
by either an intra- or intermolecular secondary metathesis
reaction at the living chain ends of the propagating species.
A small amount of another carbene species X giving a broad
signal at 17.44 ppm, is also formed which is extremely
stable in solution. The species X is found to be an active
metathesis species and is able to perform ROMP on strained
cyclic olefins. The extent of regeneration is found to
increase as the steric bulk of the substituent in the 7-position
increases.
1H NMR spectra were recorded on a Varian Mercury 400 or
a Varian Inova 500. Chemical shifts are quoted in ppm,
relative to tetramethylsilane (TMS), using TMS as the
internal reference. 13C NMR were recorded using broad
band decoupling on a Varian Mercury 400 or Varian Inova
500 at 100 and 125 MHz, respectively. Electron impact (EI)
mass spectra were recorded on a Micromass Autospec
spectrometer operating at 70 eV with the ionisation mode as
indicated.
Elemental analyses were obtained on an Exeter Analytical
Inc. CE-440 elemental analyser.
ROMP of oxygen-containing norbornene monomers with-
out alkoxy groups in the 7-postion (4a, 4b, 5a and 5b) and
also monomers with alkoxy groups in the 5 and/or 6
positions of norbornene (6 and 7) have been performed
under similar conditions. None of these systems exhibited
regeneration of the initiator and no resonances due to
species X can be seen in the 1H NMR spectra. This suggests
that the specific position of the alkoxy functionality plays a
vital role in the regeneration of the initiator and that it has a
pronounced influence on the formation of species X.
1
4.2. General procedure for H NMR scale ROMP
reactions
All ROMP reactions were prepared in a Braun glove box
under an inert atmosphere. Initiator 1 (10 mg) was dissolved
in deuterated solvent (0.4 mL) and stirred for 5 min. The
relevant monomer was dissolved in deuterated solvent
(0.4 mL). The monomer solution was injected into the
initiator solution and stirred for 5 min. The solution was
transferred to an NMR tube fitted with a Young’s tap, which
allowed the vessel to be closed under a nitrogen atmosphere.
A change in the polarity of the solvent has no significant
effect on the amount of initiator initially consumed or on the
extent of regeneration of the initiator, but the overall
kinetics for the polymerisation process are retarded.
1
The reactions were monitored by H NMR spectroscopy
every 15 min for the first 3 h and then at longer periods until
no further reaction was observed. In all cases the integrated
intensities of the alkylidene signals were compared to that
of the TMS signal, which was assumed to remain constant
throughout each experiment.
It is concluded that regeneration of the initiator and the
formation of stable ROMP active alkylidene species is
dependent on the position of the alkoxy functionality within
the monomer unit. This could be attributed to the ability of
the oxygen to coordinate efficiently to the ruthenium metal
centre when it is specifically situated in the 7-position of the
norbornadiene monomers.
4.2.1. Preparation of 7-iso-propoxynorbornadiene [2b].
Compound 2a (6.94 g, 42.3 mmol) was dissolved in propan-
2-ol (50 mL) under an inert atmosphere and sulphuric acid
(7 mL) dissolved in propan-2-ol (50 mL) was added
dropwise with stirring. The solution was heated to 40 8C
and stirred for 3 days. The reaction mixture was poured onto
ice (75 g) and extracted with dichloromethane (3£25 mL).
The combined organic layers were washed successively
with saturated solutions of NaHCO3 (3£50 mL) and NaCl
(3£50 mL). After drying over MgSO4 and filtering, the
solvent was removed under vacuum and the residue was
purified by fractional distillation under reduced pressure to
We are currently trying to elucidate the chemical structure
of species X and the mechanism by which it performs
ROMP. The results of these studies will be published
elsewhere.
4. Experimental
4.1. General
1
afford 2.68 g (52–54 8C/18 mbar) of 2b (yield 42.3%). H
NMR (400 MHz, CDCl3): d 6.64 (t, 2H, J¼2.4 Hz), 6.56 (t,
2H, J¼1.6 Hz), 3.70 (s, 1H), 3.51 (m, 1H, J¼6.4 Hz), 3.48
(m, 2H, J¼2.0 Hz), 1.10 (d, 6H, J¼6.4 Hz) ppm. 13C NMR
(100 MHz, CDCl3): d 139.9, 137.4, 108.0, 70.4, 54.1,
22.7 ppm. Anal. calcd for C10H14O: C, 79.96; H, 9.39.
All reagents used were of standard reagent grade and
purchased from Aldrich or Lancaster and used as supplied
unless otherwise stated. THF and CDCl3 (99.9%D, 0.03%
v/v TMS) were dried over sodium/benzophenone and P2O5,

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D. M. Haigh et al. / Tetrahedron 60 (2004) 7217–7224
Found: C, 79.79; H, 9.33. MS (EI): m/z¼149.0 [M2H]þ,
135.0 [M2CH3]þ, 106.9 [M2CH(CH3)2]þ, 91.2
[M2OCH(CH3)2]þ.
References and notes
1. Furstner, A. Alkene Metathesis in Organic Synthesis; Springer:
Berlin, 1998.
4.2.2. Preparation of 7-ethoxynorbornadiene [2c]. Com-
pound 2a (20.6 g, 0.125 mol) was dissolved in ethanol
(200 mL) under an inert atmosphere and sulphuric acid
(14 mL) was added dropwise. The solution was heated to
30 8C and stirred for 5 h. The reaction mixture was poured
onto ice (150 g) and extracted with dichloromethane
(4£25 mL). The combined organic layers were washed
successively with saturated solutions of NaHCO3
(3£50 mL) and NaCl (3£50 mL). After drying over
MgSO4 and filtering, the solvent was removed under
vacuum and the residue was purified by fractional distilla-
tion under reduced pressure to afford 2.75 g (48–50 8C/
18 mbar) of 2c (yield 16.1%). 1H NMR (400 MHz, CDCl3):
d 6.63 (m, 2H, J¼1.2 Hz), 6.57 (m, 2H, J¼1.2 Hz), 3.65
(m, 1H, J¼0.8 Hz), 3.52 (m, 2H, J¼2.0 Hz), 3.37 (q, 2H,
J¼7.2 Hz), 1.13 (t, 3H, J¼7.2 Hz) ppm. 13C NMR
(100 MHz, CDCl3): d 140.1, 137.3, 109.1, 64.0, 53.1,
28.5, 15.4 ppm. Anal. calcd for C9H12O: C, 79.37; H, 8.88.
Found: C, 79.21; H, 8.63. MS (EI): m/z¼136.0 [M]þ, 106.9
[M2CH2CH3]þ, 91.3 [M2OCH2CH3]þ.
2. Ivin, K. J.; Mol, J. C. Olefin Metathesis and Metathesis
Polymerisation; Academic: San Diego, 1997.
3. Anderson, A. W.; Merkling, N. G. US Patent 2,721,189, 1955.
4. Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H. J. Am. Chem.
Soc. 1992, 114, 3974.
5. Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2039.
6. Schwab, P. E.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc.
1996, 118, 100.
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DiMare, M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875.
8. Furstner, A.; Liebl, M.; Lehmann, C. W.; Picquet, M.; Kunz,
R.; Bruneau, C.; Touchard, D.; Dixneuf, P. H. Chem. Eur. J.
2000, 6, 1847.
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Catal. 2002, 344, 597.
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Chem. Soc. 1997, 119, 3161.
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North, M. Chem. Commun. 1997, 1097.
4.2.3. Preparation of exo-5-methoxymethylnorbornene
[6]. Under an inert atmosphere, exo-5-methanolnorbornene
(3.20 g, 25.8 mmol) dissolved in dry THF (10 mL) was
added dropwise to a stirred solution of NaH (0.77 g,
32.2 mmol) in dry THF (30 mL). After complete addition,
the solution was stirred for 30 min. Methyl iodide (9.14 g,
64.4 mmol) was added dropwise to the solution and a slight
exotherm was observed. The reaction was stirred at room
temperature for 2 h. Water (,5 mL) was added dropwise to
quench any remaining NaH. The solution was poured onto
ether (250 mL) and filtered. It was then washed with water
(4£100 mL) and dried over MgSO4. After filtration, the
solvent was removed under vacuum to yield the crude
product (3.88 g) as a yellow oil. The residue was purified by
fractional distillation under reduced pressure to afford
13. Schrock, R. R.; Feldman, J.; Grubbs, R. H.; Cannizzo, L.
Macromolecules 1987, 20, 1169.
14. Murdzek, J. S.; Schrock, R. R. Macromolecules 1987, 20,
2640.
15. Bazan, G. C.; Schrock, R. R.; Khosravi, E.; Feast, W. J.;
Gibson, V. C. Polym. Commun. 1989, 30, 258.
16. Bazan, G. C.; Khosravi, E.; Schrock, R. R.; Feast, W. J.;
Gibson, V. C.; O’Regan, M. B.; Thomas, J. K.; Davis, W. M.
J. Am. Chem. Soc. 1990, 112, 8378.
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1999, 1209.
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Macromol. Chem. Phys. 2001, 202, 3624.
19. McMurry, J. Organic Chemistry; 4th ed.; Cole: Brooks, 1998;
p 204.
1
1.81 g (68–72 8C/45 mbar) of 6 (yield 50.8%). H NMR
(400 MHz, CDCl3): d 6.10 (dd, 1H, J¼5.6, 2.8 Hz), 6.05
(dd, 1H, J¼5.6, 2.8 Hz) 3.42 (dd, 1H, J¼9.2, 6.4 Hz), 3.36
(s, 3H), 3.29 (t, 1H, J¼8.8 Hz), 2.80 (br. s, 1H), 2.73 (br. s,
1H), 1.68 (m, 1H), 1.31 (q, 2H, J¼4.4 Hz), 1.24 (dt, 1H,
J¼11.6, 2.0 Hz), 1.11 (dt, 1H, J¼11.6, 4.0 Hz) ppm. 13C
NMR (100 MHz, CDCl3): d 136.8 (2), 136.8 (0), 77.8, 59.0,
45.2, 43.9, 41.7, 39.1, 29.9 ppm. Anal. calcd for C9H14O: C,
78.21; H, 10.21. Found: C, 77.83; H, 10.04. MS (EI):
m/z¼138.0 [M]þ, 123.0 [M2CH3]þ, 107.0 [M2OCH3]þ,
90.9 [M2CH2OCH3]þ.
20. Bielawski, C. W.; Grubbs, R. H. Macromolecules 2001, 34,
8838.
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Acknowledgements
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We thank EPSRC for financial support (D.M.H.) and
Catherine Heffernan for her help in obtaining NMR spectra.